Method of manufacturing centrifuge discs by electrochemical machining



Nov. 5, 1968 SHARP T. D LES METHOD OF MANUFACTURING CENTRIFUGE DISCS BYELECTROCHEMICAL cumme Filed April 2 1965 INVENTOR.

THOMAS D. SHARPLES W I ATTORNEY United States Patent I 3,409,521 p vMETHOD OF MANUFACTURING CENTRIFUGE" DISCS BY ELECTROCHEMICAL MACHININGThomas D. Sharples, Lansdale, Pa., assignor to 'Pennsalt ChemicalsCorporation, Philadelph ia,=1?a;, a corporation of Pennsylvania I FiledApr. 22, 19 65, Ser. No. 449,965 f 6 Claims. (Cl. 204143) I ABSTRACT THEDISCLOSURE 1 Centrifuge discs are madeby s uli'n'g a discblankoffrusto-conical shape to an electrode and placing an electrode ofopposite polarity 'in spaced opposing relation theretoimasking offportionsiofthel'disc which areitofbecome protruding spacer portions onthe,, disc,' flowing an electrolyte through the space between thedisc'blank} and the electrode of oppos'itefpolarity, and passing anelectric current between the two electrodes in order toelectrochemically machine ing portions.

.This invention relates to centrifuge discs. More specifically. thisinvention relates to frusto-conical discs .adapted to be stacked andpositionedinside a centrifuge bowl to increase the separatingefliciency; The inventionparticularly relates to -a centrifuge dischaving special sanitar features and to a process for making such adisc.

The prior artisreplete with centrifuge bowlsaofithe solid type adaptedto be run continuously. In operation such solid bowl centrifugescontinuously receive a feed mixture. Centrifugal force will. move theheavier particles outward toward the periphery of. thebowlwhile the.lighter particles will be displacedinwardly. In-such an operationefiiciency is low because each lighter particle disposedad: jacent theperiphery of the bowl as it'moves inward bucks the outward movement ofthe heavier particles, and viceversa. v p

To improve eflicie ncy a stack of frusto-conical discs, one nestedwithin the other, is provided in the bowl. The outwardly flowingparticles form an outwardly flowing layer on the underside ofeachfrusto-gonical disc while the inwardly moving lighter particles form aninward layer on the upper side of each disc.. In this mannerthe3,409,521 trea e oer-.5112

In most 'cases "the frusto-conical' b'ody' portion ofj the disc hasbeen'a stamping -'of sheet metal formed from a flat sheetand drawnto'the frusto-conical fshapefAlter n'ativcly, the discs, especially inthe large dimensions,'have been cut from a flat sheet and spun about a'mandrel.

A common wayof forming the spacing element-to the individual disc-memberhas been to cutout individual strips and secure them in a radialdisposition to the top of the disc elements by spot-welding techniques.This, how- 'ever, is a multi-ste'ppr'o'cedure and has a primaryobjection in that cracks appear between the 'spacing'ele'ment and theindividual disc members'These cracks provide away the space between theprotrudopenings in' which process' fiuids may 'stagnate andco'ntaminatethe subsequent process fluid. Such ctacks are difficult to clean. Insanitary applicatlhns, for"inst ance, milk purifying, the condition isextremely serious.- To over' come this objection soft solder: has beenplaced along the juncture between' the sides of the spacers andthe'discs to'create' fillets to keep out contaminants and'make the discseasier toclean. However, this hasadded yet another step to the alreadycomplicated and expensive disc-manufacturing procedure.

Spot-welding techniques for securing the spacing elements to the discmember have also been objectionable in that certain metals of which theparts must occasionally be made are weldable only in certain inertatmospheres.

1 Also the metallurgy of such metals has broken down a during thewelding.

- Another common way to form spacers has been to raise a protuberance onthe upper surface of the disc.This is disclosed in US. Patent 1,474,379.In making stacks of discs formed in this fashion the discs are staggeredto avoid inward and outward movement of the respective layers,

are efliected without the hindrance of the, oppositely moving particles.This results in greatly improved efficiency, There have been mayvarieties of discs disclosed in the prior'art. Almost all of thesediscsincorporate as an integral portion of their structure or as a separateattachment spacer elements, usually radial, which extend upward from thetop surface. of the frusto-conical disc. :These spacer elements serve tohold each disc apart from theone above it so that there is afrusto-conical channel in between the two adjacent discs permitting thepreviously mentioned layer' movement therebetween. Each of the discs ofthe prior art have also been provided with central openings adapted toreceive the centrifuge center tube. The openings have radialslotswhichreceive a key-on the center tube to hold the discs'inrotation' 'with'the centrifuge bowl. The slots and key also assurethaton the coincidence of a proturberance with an indentation on theunderside of the'disc above. An objectionto this method of making discsis the turbulence caused by the indentation on the underside of thediscs. 1

. Spacing elements havealso been provided by actually puncturing thediscs and bending on a metal staple-like applianceto serve as a spacer.Such'an arrangement" is shown in the U8. Patent 1,026,271. Y

In many cases the spacing elements serve as vanes to assure the rotarymovement of the fluidwithin the disc stack. For reasons well recited inthe prior art, it has occasionally been desirable to make the spacingelements of arcuate shape and secure them to the top of disc stackmembers. This procedure has involved individual plotting and cutting ofthe spacing elements and carefully securing them to the top of theindividual disc member. Slight irregularities in the shape of 'theindividual spacing. elements have raised a balancing problem and even'this expensive and complicated manufacturing procedure has not producedan entirely satisfactory product. Therefore it rnay readily be seen thatfor years the art has searched for a suitable process formanufacturingcentrifuge discs having integral spacers, a process thatwould be simple and inexpensive and produce an integral sanitaryproduct.

' 1 The present invention provides the answer for which reassembly thediscs will 'be returned to'the -dis'c"stack in the same radialorientation in which they were dis-*- as'sembled. This is: importantsince balance is"extremely significant in centrifuges of high speed. Inaddition, 'it' assures alignment of the spacer elementsone on'top of theother so that'the stack is not springy under compression; "*1 Methodsfor producing the discs which-comprise' the disc stack of the irior=arthave been many varied.

the art has been seeking. It involves a centrifuge disc electrode andplacing an electrode of opposite polarity in spaced opposing relationthereto, masking'off por-' tions of the disc which are to become theprotruding rp'ortio'ns, flowing an electrolyte through 'the space be-'tween the disc blank and the electrode of opposite polarity and passingan electric current between the .two electrodes to electro-chemicallytween the spacers.

machine away the space .be-'

g per electrode positioned thereabove;

Other features of the invention will be understood from a reading of thefollowing specification and reference to the drawings in which:

FIGURE 1 is a schematic view representing a frustoconical disc blankmounted on an electrode with the up- FIGURE 2 is an enlarged fragmentarysectional view of a portion of the disc blank which will form aprotruding portion such as a spacer element and clamped into theelectro-chernical machining device;

FIGURE 3 is an enlarged fragmentary sectional view taken on the line 3-3of FIGURE FIGURE 4 is an enlarged fragmentary sectional view taken onthe line 4-4 of FIGURE 5;

FIGURE 5 is a top plan view of a centrifuge disc made in accordance withthe process described herein; and

FIGURE 6 is a top plan view of an alternate form of centrifuge disc madein accordance with the process described herein.

Referring more specifically to the drawings, FIGURE 1 shows in schematicfashion a portion of the aapparatus by which the centrifuge discs'herein are manufactured. The apparatus comprises an upper electrodewhich may, for instance, be the anode A and a lower electrode which maybe the cathode B. These electrodes comprise the socalled tools formaking the product described herein. In operation a stamped or spun discblank 10 is mounted on one of the electrodes, for instance, electrode B.A plastic cup C may be set on top of electrode B and be shaped toexactly receive the slotted opening of the blank. This orients the blankand keeps the edges about the opening from being e'lectro-chemicallymachined. The electrodes are drawn together until the blank is clampedtherebetween. The electrode A is provided with insulating strips D whichmay protrude downward from the underside of the electrode and correspondto the areas of the finished centrifuge discs which are raised, as toform the spacing elements.

The upper electrode A is provided with a central opening B through whichelectrolyte flows. As shown in the sectional view FIGURE 2, theelectrolyte flows preferably under considerable head into the spacebetween the blank 10 and the upper electrode A. In actual operation theelectrolyte may comprise a salt solution, aqueous mineral acid, causticpotash or caustic soda in aqueous solution. Various additives may beused in the electrolyte to effect results well known in the art. It willbe seen that the insulator strip D tightly engages the upper surface ofthe blank and masks off what is to 'become the spacing element 12 fromthe electro-chemical machining operation.

With the electrolyte flowing in the channels between the upper electrodeand the blank, electric current is passed between the two electrodes.The current density may vary in accordance with the material of theblank and the results to be obtained. If the discs are to be made out ofsteel, for instance, a current density of 1100 amps. per square inch maybe used to elfect a penetration rate on the order of 0.1 inch perminute. If the blank is made from aluminum a slightly higher density,such as 1190 amps. may be employed to achieve the same rate. Dependingon the size of the disc to be made and the height of the spacers to beformed an appropriate rate and time of exposure may be selected by oneskilled in the electro-cheinical machining art. It will be noted fromFIGURE 2 that the electro-chemical machining process will remove themetal from the upper surface of the blank which is not covered by theinsulator D.

It should be understood that an electrolyte after passing throughchannels between the upper electrode and disc may be purified to havemetal particles and other foreign matter removed. This material may beferric hydroxide for instance in the processing of steel. The purifiedelectrolyte is returned to the machining apparatus for passage throughthe opening E and is reused.

In view of the fact that the blank which is to be rnachined is offrusto-conical shape, it will be apparent that the coverage of theelectrolyte toward the center of the disc will be much greater thanadjacent the outer periphery. In discs of diameter of say 2 /2" thiswill make no difference. But in making larger discs it may be desirableto supply additional electrolyte through apertures in the upperelectrode spaced outward from'the center at locations immediately aboveportions of the blank.

The sectional view of FIGURE 3 shows the product which results from theabove-described process. The disc 10 is provided with the upwardlyprotruding spacer element 12 which is an integral part of the disc. As'an example the disc will have a thickness between spacers of DOS-.035inch. The spacer may be .007-.150 inch thick additionally. Actualdimensions will be specified according to the use to which the disc isput. A fillet 14 is formed in the electro-chemical machining operationbetween the respective sidewalls of the spacer element and disc body.This fillet is especially significant in sanitary operations since itprecludes the accumulation in the area of process solids which thecentrifuge is separating, It also makes the disc easier to clean. Thefillet will most desirably have a radius in the range of .005 to .025inch, although greater radii are obtainable by appropriate adjustment ofthe machining technique.

Another benefit of the invention is shown in FIGURE 4 wherein theuppermost portion of the disc terminates in an inward horizontal flange10a which may be of various thickness depending on whether or not it ismasked off by an insulating body during the electro-chemical machining.It will be understood that the height of the flange will control theheight of the opening between flanges on adjacent discs so that theannular passage between adjacent discs at their inner periphery may becontrolled thereby. Therefore, if it is desired to have a large flowof'fluid through this annular opening, the flange may not be maskedduring the machining. This will result in a flange having approximatelythe thickness of the disc between adjacent spacers. If alternatively alimited flow is desired, masking may be used and a thicker flange (shownin phantom) may result. a a

Reference to FIGURE 5 shows that the central portion of the disc isstamped out to provide positioning of the discs in a stack about thecentrifuge center tube. This is preferably done prior toelectro-chemical machining. A number of slots 20 are alsostarnped in thedisc about the central opening to mate with correspondingly positionedkeys on the centrifuge center tube to assure proper reorientation of thediscs. One slot and key may be shaped differently if desired to assureonly one correct radial orientation of the discs.

It should be here noted that one of the advantages of the processdescribed in that the surfaces which have been machined away by theelectro-chemical method are smooth and polished and require no furtherfinishing prior to their use in the machine. In an actual product thefinish is at least substantially equivalent to a number 7 highlusterfinish as applied to sheet work. This is obviously an expense savingfeature since it makes unnecessary such hand finishing.

If flow distribution openings are desired in the'disc, they may be alsoelectro-chemically machined.

FIGURE 6 is a modified form of disc 10' made by the process describedherein. The primed form of reference numerals are used. In the modifiedform the spacers 12' are arcuate in shape. In the prior art it wasnecessary to carefully plot and cut out each such spacing element andsecure them with painstaking care tothe top of the disc member. Inaccordance with the present invention the machining away of portionsbetween the spacers is accomplished electro-chemically and the arcuatespacers are achieved by the provision of correspondingly arcuateinsulating elements D which mask the upper'surface of the blank. Throughthis simple one-step procedure successive discs are identical and haveexactly the same balance characteristics.

It should be understood that the present invention has otherapplications, that virtually any kind of centrifuge disc provided with aspacer may be manufactured in accordance with the present description.The process may be used to provide bafiles for centrifugal extractorsand vanes for centrifuges of the so-called vane-stack type. A widevariety of metals may be used: aside from steel, aluminum, titanium andnickel and alloys thereof are entirely workable in accordance with theinvention;

Further, especially on large diameter discs the upper electrode insteadof having spacers D may have slots masked with plastic to avoidelectro-chemical machining of the blank in these areas. An electrode ofthis type may at the beginning of the machining operation be spaced fromthe blank and advance slowly down toward the blank as the machiningprogresses.

Therefore it is to be understood that the above particular descriptionis by way of illustration and not limitation, and that changes,omissions, additions, substitutions, and/or other modifications may bemade without departing from the spirit of the invention, Accordingly, itis intended that the patent shall cover, by suitable expression in theclaims, the various features of patentable novelty that reside in theinvention.

I claim:

1. A method for making a centrifuge disc comprising a frusto-conicalmetal body having a central opening and a polished surface on said bodyportion, integral protruding spacer elements having walls risingsubstantially perpendicularly from the said polished surface of the bodyportion, integral fillets disposed between the walls and the saidpolished surface, the said polished surface, the spacer elements and thefillets being formed in an electrochemical machining operation, saidmethod comprising: providing a frusto-conical blank having a convexconical surface, providing an electrode having a concave conical surfaceadapted to mate with said convex conical surface, said electrode havinga plurality of insulating strips spaced about said concave surface,moving said electrode into proximity with said blank so that saidinsulating strips are contiguous with said convex surface whereby todefine a plurality of gaps between said convex and concave surfaces;fiowing electrolyte through said gaps, applying a source of electricalenergy to make said blank predominantly anodic whereby said blank iselectrolytically etched and containing said application of saidelectrical energy until said blank is etched to a depth of at least0.007 inch.

2. A method as described in claim 1 wherein the fillets have a radius inthe range of .005-.025 inch.

3. A method as described in claim 1 wherein said polished surface has afinish at least substantially equivalent to a number 7 high-lusterfinish as applied to sheet work.

4. A method as described in claim 1 wherein the body portion presents aninward flange about the central opening, the flange having a thicknesssubstantially the same as the body portion between adjacent spacers.

5. A method as described in claim 1 wherein the insulating strips andthe resulting spacer elements are arcuate.

6. A method as described in claim 1 wherein the blank is comprised of ametal selected from the group consisting of steel, nickel, titanium andaluminum.

References Cited UNITED STATES PATENTS 961,349 6/1910 Hartman 233-29 X1,376,365 4/1921 Wertheimer 204-143 2,012,589 8/ 1935 Miller 233-29 X2,599,619 6/1952 Eckers 233-47 X 3,056,734 10/1962 Scott 204-1433,239,441 3/1966 Marosi 204-143 3,288,699 11/1966 Trager et a1. 204-143FOREIGN PATENTS 840,544 7/1960 Great Britain.

RQBERT K. MIHALEK, Primary Examiner,

